He confessed the letter first.

On the day of that first visit, he said, Irene had tried to call her mother the instant they walked out of the clinic doors — had actually had the phone in her hand, Martha’s contact already pulled up.

And Mark had stopped her.

He had talked her out of the call, and somewhere in the maneuvering he had ended up with the letter she’d written, and he had kept it.

Why had he stopped the call?